1. Field of the Invention
The present invention relates to a vehicle braking system and a vehicle braking method, and more particularly to vehicle braking that is effected using both a regenerative braking device and a friction braking device.
2. Related Art
In recent years, electric vehicles are known as friendly vehicles to the global environment. In general, in an electric vehicle, a motor is driven by electricity power supplied from a battery to thereby generate a driving force in a wheel. On the other hand, at the time of braking, the motor, which is a drive source, is used as a generator to convert kinetic energy into electric energy to thereby recover the energy. At the time of generation like this, a load corresponding to the amount of electricity power generated by the motor is applied to the wheel so as to perform regenerative braking to thereby generate a braking force in the wheel. For example, JP-A-10-203351 discloses a method for controlling the regenerative braking and friction braking in which a braking force is provided by adjusting a frictional force via hydraulic pressure in a cooperative fashion. In the method of JP-A-10-203351, a maximum value of the regenerative braking force is calculated from the charged status of the battery, and a balance between the regenerative braking force and the friction braking force is determined appropriately based on the result of the calculation so as to satisfy a required braking force that is required for the wheel.
However, in the method of JP-A-10-203351, a feed forward control is performed by estimating both a regenerative braking force and a friction braking force which are to be given to the wheel. Therefore, a braking force actually applied to the wheel is only estimated. As a result, it is difficult to perform the cooperative control with high accuracy.